(1) Field of the Invention
This invention concerns fire resistant adhesive resins that include a halogen-free and bromine-free flame retardant ingredient. This invention also includes conductive foils coated with the halogen-free fire resistant adhesive resin coated compositions of this invention as well as printed circuit boards manufactured using the adhesive resin coated conductive foils.
(2) Description of the Art
Prepregs, resin coated conductive foils, reinforced cores, and other substrates used in the manufacture of circuit boards typically include a resin component. Many of the resin ingredients are flammable. Therefore, flame-retardant ingredients are added to resins prior to use in order to produce flame retardant circuit board substrates and laminates. Commonly used flame retardant components are those that include a halogen such as bromine.
The use of halogen containing flame-retardant compounds in circuit board substrate resin formulations may create problems with disposal of used circuit board components. There is some concern that halogens such as bromine compound can leach from circuit board components following disposal in landfills. Therefore, there is a need for adhesive resin formulations that include a halogen free flame-retardant. In addition to being halogen free, there is a need for retardant fire resistant halogen-free adhesive resin compositions that produce circuit board substrate materials with high Tg""s, low Dk""s and low moisture absorption properties.
It is an object of this invention to provide a resin composition that includes a halogen free flame retardant composition. The composition is specifically formulated to chemically interact with surrounding thermoset resin matrix components to hasten curing kinetics (peak exotherm temperature) while preserving most of the system latency and to react with the resin ingredients to become an integral part of the cured resin backbone matrix. This feature of the compositions of the present invention enhances the 2-step coating manufacturing process described below and helps to minimize resin movement though faster C-staging and increase production rates.
It is another object of this invention to provide a conductive metal foil that is coated with a resin composition that includes a halogen free flame retardant composition wherein the resin coated conductive foil has good peel strengths.
It is still another object of this invention to provide resin coated conductive metal foils that are useful in the manufacture of circuit boards and other electronic laminates.
In one embodiment, this invention is a flame-retardant adhesive resin composition comprising at least one resin and from about 12 to about 17 wt % melamine cyanurate having a particle size of from about 1 micron to about 12 microns.
In yet another embodiment, this invention is a conductive metal foil having a first surface and a second surface wherein the first surface includes a flame-retardant resin layer comprising at least one resin, and at least one halogen-free flame retardant composition wherein the resin composition includes essentially no halogen containing flame-retardant compositions.